1. Field of the Invention
The invention relates to a network arrangement, network device and method for the prioritization of real-time telegrams in a convergent network, in particular in an industrial network, wherein the convergent network has at least one central distribution infrastructure and at least one decentralized distribution infrastructure and wherein in the convergent network at least one service sends and/or receives real-time telegrams, and wherein the convergent network has at least one switching node which is a central network node for the connection of central distribution infrastructure and decentralized distribution infrastructure, and which has at least one coupling port via which the switching node is connected to the decentralized distribution infrastructure, wherein the switching node has a central network port via which the switching node is incorporated into the central distribution infrastructure.
2. Description of the Related Art
Prioritization methods can be used in many industrial sectors, in particular in the automation and automobile industry and in the energy sector where there is a requirement for communication networks to be appropriate for all communication services throughout the plant, from fieldbus level through to business level, based on the a single standardized protocol. Such a communication network is also described as a convergent network in which various services and real-time services can be realized. Such networks are also described as convergent “time-sensitive networks” (TSN). Communication based on the Ethernet protocol can be mentioned here as an example of this in the industrial sector.
A central distribution infrastructure, also known as a backbone, is the central part of the convergent network. The majority of the data is distributed to the corresponding decentralized distribution infrastructures via this central distribution infrastructure. The backbone may also consist of a number of independent or interconnected central distribution infrastructures. As a rule, the performance of the central distribution infrastructure (of the backbone) is significantly higher than that of decentralized distribution infrastructures. In addition, corresponding redundancies may be provided in the central distribution infrastructure.
The coexistence of various services results in several challenges. These services include cyclic data traffic, such as the continuous transfer of control data (also control data streams or CD streams) and audio-video streams (also AV streams) and acyclic data traffic, such as best effort traffic (BE traffic), which should be transferred at the best speed currently possible for this service.
In spite of the coexistence of a number of services in the same network, for real-time services, such as for industrial control systems and their real-time telegrams, for each path between a control device and terminal equipment, predefined requirements such as minimum delay times (low latency), minimum deviations from the operating cycle and minimum deviations in the runtime of data packets (low jitter) must be met and furthermore, adequate bandwidth and sufficient resources must be available. Requirements such as these are generally summarized under “quality of service” (QoS). These requirements must also be met when a number of real-time services access a common central distribution infrastructure.
Hitherto, ingress policing at the input ports and egress policing at the output ports have prevented cyclic data streams, such as CD streams or AV streams, from using more than the bandwidth reserved for them via known mechanisms such as leaky bucket. If, for example, a data stream has used its reserved bandwidth, then its telegrams are deleted for a certain period of time. Thus, the greater data load at a switching node has been taken into account hitherto compared with the coupling ports at the central network ports (also backbone ports). Switching nodes are the network nodes or distributors which connect the central distribution infrastructure to the decentralized distribution infrastructures, coupling ports are the ports at which a decentralized distribution infrastructure is connected to the switching node.
Hitherto, with the known policing mechanisms (e.g. leaky bucket) more bandwidth has been reserved for real-time services at the central network ports than for real-time services at the coupling ports. If the respective bandwidth reserved is not used, unnecessary reserves may exist, which can be uneconomical. However, if the reserved bandwidth is used, real-time telegrams of this service are deleted for a period of time and the guaranteed and timely delivery of telegrams can no longer be ensured. The “Quality of Service” requirements cannot be met thus either.